The Lapp Knot

and its Evil Impostor

July 27, 2010

The Lapp knot, a bend,  is not well presented on the web.  At least one YouTube video teaches an unreliable and hazardous version of it.  Several other depictions of the knot do not clearly discriminate between the more and less reliable versions of it.   Even if these errors of presentation were not so prominent, the existence of  a hazardous knot that looks almost identical to the Lapp knot, and which can be tied by a simple error when attempting to tie the Lapp knot, means that it is questionable whether the knot should be widely taught to non-experts. The look-alike impostor of the Lapp knot, is called the anti-Lapp knot in the following illustration. It merits the name evil impostor because it's hazardous, hard to tell from the Lapp knot, and easy to make by mistake while you're trying to make a Lapp knot..
Lapp-knot-and-anti-Lapp-knot.jpg.

As shown in the illustration, both standing parts of the Lapp knot must come out of the same side of the knot when it is in the form it takes just before dressing it into working form.

The anti-Lapp knot can fail catastrophically under load, one working end slipping through the knot until the knot evaporates into nothing.  I tested both knots in 1/16 inch / 1.6 mm nylon braided cord.  I used a test rig consisting of a dowel foot bar and a dowel handle, allowing me to use the strength of my legs to tension a test specimen.

I tested  a dozen Lapp knots and a dozen anti-Lapp knots.

None of the Lapp knots failed under a heavy load that stretched the cord by at least 25%, and none slipped even a little.

Every one of the anti-Lapp knots failed under moderate load by slipping away into nothing.

(Thanks to roo for "evil impostor".)

References: 

See the discusion of the Lapp knot at the International Guild of Knot Tyers forum.

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